1. Field of the Invention
The present invention relates to wireless radio transmission of voice and data information.
2. Background of the Invention
Cellular telephone systems have gained widespread acceptance as an efficient means of mobile voice and data communications. While early mobile units were large and complex, miniaturization has made possible hand-held units with full functional capabilities allowing the user freedom to use the phone unit without connection to the vehicle. Unfortunately, this miniaturization has made portable and or hand-held units less practical for vehicular use. For example, battery charging, remote antenna connections, voice and data communications, and most importantly, what is known as "hands free" operation require physical connection to the phone unit.
To solve this problem cellular phone manufacturers have made available car kits to provide the required features. These kits include physical hardware to retain the phone in the vehicle including an attachment for establishing an electrical connection to the phone and various types of remote speakers, microphones and external antenna connections. The speakers and microphones provide "hands free" operation, and the external antenna connection improves reception of RF signals in the highly metallized automobile environment. These kits also include complex electronics modules to provide a variety of battery charging and audio amplification services to the phone unit.
There are a large number of models of cellular telephones in existence and each physical interconnection and electrical interface is unique to a manufacturer's specific model. There are many examples of presently used physical interconnections. As a result, car kits do not provide any form of universal connection and are neither physically nor electrically interchangeable. Further, because of the large variety and relatively low volume production of these kits, users are forced to pay prices comparable to the much more complex phone unit itself to obtain these kits.
This situation has caused a hardship on cellular telephone users and affected the marketplace for new equipment. Fleet users, for example, cannot provide a universal car kit connection for the variety of phones they may acquire. Users are forced to abandon their investment in the car kit when purchasing new models of telephones. These limitations have prevented businesses such as car rental agencies from providing users with means to use their car phones in rented vehicles. Further, the high cost of these car kits has caused many users to operate hand-held units while driving, an unsafe condition which is subject to increasing governmental concern and regulation.
In addition, recent advancements in the field of electronics has made it desirable to be able to transmit and receive digital data using a cellular phone. Modern communications networks, notably cellular radio telephone systems, have allowed the possibility of wide area networks for digital data transfer and control. At present, data communication is conventionally accomplished via analog channels with Advanced Mobile Phone Service (AMPS) type (FM) phones. In order to send digital information, modems are used to convert digital signals to analog tones which are sent through the phone via the normal wireless radio voice channel. AMPS type phones also include a digital channel for transceiving command and control signals to and from the phone circuitry. However, no output pin is currently provided for transferring digital information beyond the phone itself.
In recent years, progress in the field of wireless personal communications has been impeded by the limited amount of assigned radio spectrum. In response, the industry has recently developed digital wireless phones which can more easily share the available RF spectrum by packetizing data. Digital wireless phones such as Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA) phones have the capability of passing digital information via a special digital data burst mode. However, both CDMA and TDMA require bandwidth compression of voice signals in order to make more efficient use of available RF spectrum. This is typically accomplished by some form of voice encoding/decoding module (often called a vocoder) which systematically reduces the number of bits per second required to be sent to represent voice signals based on a predetermined knowledge of the workings of the voice tract. By optimizing the coding process for voice signals, the transmitted bit rate can be reduced from several tens of kilobits per second to a few kilobits per second, thereby making more efficient use of the available RF spectrum.
Since the vocoders are designed specifically to work with voice signals, they cannot accommodate modem, facsimile, or other signals that do not exhibit voice characteristics. Data signals must be sent in a different fashion, ideally as digital signals. Neither the conventional AMPS cellular telephones nor the new analog/TDMA dual-mode cellular phones presently provide a digital data path into or out of the phone.